Japanese Laid-Open Patent Publication No. 2006-311065 discloses a function of detecting an original paper size, and when the function is used, an original can be copied (printed) with a paper size corresponding to a detection result.
When the function is used, in a case where a bundle of originals in which original paper sizes are different, the bundle of originals is set on an Auto Document Feeder (ADF) and copying is instructed, a copy is automatically made in accordance with an original paper size.
However, when an image forming apparatus erroneously performs original paper size detection, for example, an original with a paper size of A4 is copied as an A3 original, and an A3 original is copied as an A4 original in some cases.
In such a case, a user is required to check all the obtained copies to confirm whether the paper size detection is correctly performed after copying a bundle of originals in which original paper sizes are different.
In a case where paper size detection has been erroneously performed for even one sheet in the bundle of originals in the above checking, it is necessary to make all the copies again, or pick up an erroneously detected original from the bundle of originals, make a copy again with a correct setting to replace the erroneously copied paper.
When a copy is made using an automatic detection function in this manner, a printing member such as copy paper or a toner is wasted in some cases, and additionally, time for making a copy again is wasted.
Meanwhile, an image forming apparatus having a so-called preview display function, for confirming by displaying a printing image (image data) on a display panel or the like before copying or printing has been proposed. The user, with the use of the preview display function, is able to confirm the printing image before making a copy to cut out the waste of the printing member or the trouble of making a copy again.
By the way, in the image forming apparatus having the preview display function, when an instruction of displaying a preview from a user is received, image data of a firstly scanned original is displayed. It is usual that the image data of the original is sequentially displayed sheet (one image data) by sheet thereafter by an instruction operation of the user.
Accordingly, in the case of scanning a bundle of originals consisting of 10 sheets of originals with the paper size of A4 and 10 sheets of A3 originals, and confirming whether or not the paper size detection of originals included in the bundle of originals is performed correctly, it is necessary to operate an instruction button (next display button) and display a preview of image data of the original sheet by sheet sequentially.
In the above example, the user needs to operate the instruction button 10 times for displaying the preview of aimed image data of the original in order to confirm whether or not the paper size detection is performed correctly on the 11th A3 original, however, such an operation is too troublesome for the user.
Meanwhile, in the case of confirming whether or not the paper size detection is performed correctly on the original, it is assumed that the user thinks that he/she may make a copy actually after displaying a preview of original image data immediately after (next) a detected original paper size has been switched, such as from A3 to A4, or original image data before (previous) or after (next) the original image data to confirm that the paper size detection is performed correctly.